As an aside, one of the most interesting aspects to this visual pathway is its entirely faithful retinotopic map. That is, information that is recieved by the eyeballs is eventually spat out to the primary visual cortex 1 for 1. No summation, no concatenation, no mixing of signals. In other words, if you had a super-duper-really-sharp scalpalTM and sliced out a single line of rods and cones from your retina, that "black line" of dead/dysfunctional nerve axons will be maintained all the way down the cabling right through to the back of your head.